Neumann Gefell CMV 563 - quite noisy !

[saint gillis]

Hello,
I've got a CMV 563, it works, but it's quite noisy.
I tested several new tubes (EC92), and I found one that had lower noise.
Changed the capacitors, made a serious PSU filtering, better, but still quite noisy.

I've read andre tchmil advising to change some resistors to improve the noise.
What about making Oliver Archut's mod?
CMV563 Schematics - Tab-Funkenwerk

 

[saint gillis]

So I did Oliver Archut's mod (keeping the original transformer), there's less noise, a bit more gain (better SNR), and it sounds more open and warm, it sounds really more like a Neumann, the guy knew what he did about mics !
Maybe the fact that I replaced the resistors also improved the noise, but the mic sounds better for sure with the mod

 

[Michael Tibes]

Interesting, good to read! The old east german devices have a lot of variation in parts quality, it might pay off to rebuild the whole amplifier with high quality parts. Something on my endless to do list...

Quite some time ago I managed to buy a replacement tube from Gefell because my Mic got noisy too. They would only sell me one and told me that meanwhile they had probably bought all stock of EC92s worldwide, tested them and passed on the ones not meeting their specs - which must have been a lot. So the chances of finding an on spec EC92 on the free market might be small. I do not recall the new tube having made a serious difference so I stopped using the mic and been wanting to rebuild the amp since because I felt it was also loosing treble. So my unconfirmed conclusion is to first make sure that the amp and psu are really up to spec and then to test the 2 tubes I have in the mic.

Michael

 

[saint gillis]

I found a nos tube (cbs) , and it also helped a bit. I've tried few used old tubes that were a nightmare..

 

[RuudNL]

I noticed that Oliver Archut was a big fan of using 1 G.ohm resistors (instead of 100 M.ohm).
This has advantages and disadvantages. A disadvantage may be a higher sensitivity to (air) humidity and a 'slower' response of the capsule. An advantage is a lower noise.
Especially with the 1 G.ohm resistors it is important to keep them absolutely clean!
Even a fingerprint on a 1 G.ohm resistor can degrade the signal to noise performance 8-10 dB!

 

[rennywilson]

First time poster, amateur tinkerer, recording studio owner here. Dealing with a noisy CMV 563 here as well. It's completely stock, with a recently reskinned m7s and mk55. Didn't notice the noise floor as much when it was living over the drums for an extended period , but now that I've been testing it on vocals with the less bright m7s i feel like the noise might be slightly too high to use on any vocalist who doesn't sing with their chest, which is a problem. I already replaced the noisey Xformer in the PSU, and I bought the AMI replacement xform for the mic itself which is not yet installed.
Because the mic is stock im hesitant to modify it to maintain its resell value, the mic itself does have a certain mojo that's unmistakably vintage that I appreciate (the mic has excelled on drum and cab micing where the noise floor doesnt really matter.)

yet...

The Archut mod is tempting, although the mics insides are virtually untouched . As for the replacement xformer - does anyone with experience putting a AMI UM351 into a noisy stock 563 and heard a noticeable improvement? Seems less invasive FWIW, i might have to just jump to it.

I'm gonna end up doing one, or the other sooner or later. Looking for encouragement and advice.

I'm actually curious how the grease in our fingerprints that can mess up the noise floor in the mod as mentined by @RuudNL

Anyway,
R.

 

[C12VR]

First time poster, amateur tinkerer, recording studio owner here. Dealing with a noisy CMV 563 here as well. It's completely stock, with a recently reskinned m7s and mk55. Didn't notice the noise floor as much when it was living over the drums for an extended period , but now that I've been testing it on vocals with the less bright m7s i feel like the noise might be slightly too high to use on any vocalist who doesn't sing with their chest, which is a problem. I already replaced the noisey Xformer in the PSU, and I bought the AMI replacement xform for the mic itself which is not yet installed.
Because the mic is stock im hesitant to modify it to maintain its resell value, the mic itself does have a certain mojo that's unmistakably vintage that I appreciate (the mic has excelled on drum and cab micing where the noise floor doesnt really matter.)

yet...

The Archut mod is tempting, although the mics insides are virtually untouched . As for the replacement xformer - does anyone with experience putting a AMI UM351 into a noisy stock 563 and heard a noticeable improvement? Seems less invasive FWIW, i might have to just jump to it.

I'm gonna end up doing one, or the other sooner or later. Looking for encouragement and advice.

I'm actually curious how the grease in our fingerprints that can mess up the noise floor in the mod as mentined by @RuudNL

Anyway,
R.

You can keep the circuit original but replace the resistors and output cap with modern spec parts. Most people know the deal with these East German mics. Definitely replace the output capacitor, unless you want a dead transformer and a saturated core. If the cap is sufficiently shitty, it might have an effect on sound. Not worth damage and unreliability, though. The market will pay a premium for the metal shell (name badge) even if the capacitors, resistors, and transformer are replaced, as long as you say "it's as good as a neumann berlin now!" and "NEUMANN KILLER!"
The noise issue may not be fixable, but maybe look into the mic tube first, then the power supply? Not the transformer, no reason that should put noise on the signal unless it's right next the the audio line, but the PSU is an old piece of crap with worn-out tubes in it. Consider upgrading to a solid state supply with better filtering less maintenance, more security. Remember that the cap values were chosen not because they were ideal but because they were the best that could be reasonably done at the time considering cost and space. Maybe not even the best, they probably had a strict budget. This might help reduce the noise floor a bit. Also maybe carefully clean the high-impedance section if it's dirty (with 99% alcohol, but whatever you do don't touch the capsule!)

The biggest "mojo" here is going to be the transformer, so if you like the sound now don't change it.

 

[MagnetoSound]

C1 is probably degraded.

 

[TLRT]

Usual probems are the mic caps and high megaohm resistors, those old rft's usually have drifted values. Check psu caps and the regulator tube too.